A novel allele of FILAMENTOUS FLOWER reveals new insights on the link between inflorescence and floral meristem organization and flower morphogenesis

<p>Abstract</p> <p>Background</p> <p>The <it>Arabidopsis </it><it>FILAMENTOUS FLOWER (FIL) </it>gene encodes a YABBY (YAB) family putative transcription factor that has been implicated in specifying abaxial cell identities and thus regulating organ polarity of lateral organs. In contrast to double mutants of <it>fil </it>and other <it>YAB </it>genes, <it>fil </it>single mutants display mainly floral and inflorescence morphological defects that do not reflect merely a loss of abaxial identity. Recently, <it>FIL </it>and other <it>YABs </it>have been shown to regulate meristem organization in a non-cell-autonomous manner. In a screen for new mutations affecting floral organ morphology and development, we have identified a novel allele of FIL, <it>fil-9 </it>and characterized its floral and meristem phenotypes.</p> <p>Results</p> <p>The <it>fil-9 </it>mutation results in highly variable disruptions in floral organ numbers and size, partial homeotic transformations, and in defective inflorescence organization. Examination of meristems indicates that both <it>fil-9 </it>inflorescence and floral meristems are enlarged as a result of an increase in cell number, and deformed. Furthermore, primordia emergence from these meristems is disrupted such that several primordia arise simultaneously instead of sequentially. Many of the organs produced by the inflorescence meristems are filamentous, yet they are not considered by the plant as flowers. The severity of both floral organs and meristem phenotypes is increased acropetally and in higher growth temperature.</p> <p>Conclusions</p> <p>Detailed analysis following the development of <it>fil-9 </it>inflorescence and flowers throughout flower development enabled the drawing of a causal link between multiple traits of <it>fil-9 </it>phenotypes. The study reinforces the suggested role of <it>FIL </it>in meristem organization. The loss of spatial and temporal organization of <it>fil-9 </it>inflorescence and floral meristems presumably leads to disrupted cell allocation to developing floral organs and to a blurring of organ whorl boundaries. This disruption is reflected in morphological and organ identity aberrations of <it>fil-9 </it>floral organs and in the production of filamentous organs that are not perceived as flowers. Here, we show the role of <it>FIL </it>in reproductive meristem development and emphasize the potential of using <it>fil </it>mutants to study mersitem organization and the related effects on flower morphogenesis.</p

Guard-cell-targeted overexpression of Arabidopsis \u3ci\u3eHexokinase 1\u3c/i\u3e can improve water use efficiency in field-grown tobacco plants

Water deficit currently acts as one of the largest limiting factors for agricultural productivity worldwide. Additionally, limitation by water scarcity is projected to continue in the future with the further onset of effects of global climate change. As a result, it is critical to develop or breed for crops that have increased water use efficiency and that are more capable of coping with water scarce conditions. However, increased intrinsic water use efficiency (iWUE) typically brings a trade-off with CO2 assimilation as all gas exchange is mediated by stomata, through which CO2 enters the leaf while water vapor exits. Previously, promising results were shown using guard-cell-targeted overexpression of hexokinase to increase iWUE without incurring a penalty in photosynthetic rates or biomass production. Here, two homozygous transgenic tobacco (Nicotiana tabacum) lines expressing Arabidopsis Hexokinase 1 (AtHXK1) constitutively (35SHXK2 and 35SHXK5) and a line that had guard-cell-targeted overexpression of AtHXK1 (GCHXK2) were evaluated relative to wild type for traits related to photosynthesis and yield. In this study, iWUE was significantly higher in GCHXK2 compared with wild type without negatively impacting CO2 assimilation, although results were dependent upon leaf age and proximity of precipitation event to gas exchange measurement

Expression of Arabidopsis Hexokinase in Tobacco Guard Cells Increases Water-Use Efficiency and Confers Tolerance to Drought and Salt Stress

Abiotic stresses such as drought and saline water impose major limitations on plant growth. Modulation of stomatal behavior may help plants cope with such stresses by reducing both water loss and salt uptake. Hexokinase (HXK) is a sugar-phosphorylating enzyme involved in guard cells&rsquo; sugar-sensing, mediating stomatal closure and coordinating photosynthesis with transpiration. We generated transgenic tobacco lines expressing the Arabidopsis hexokinase1 (AtHXK1) under the guard cell-specific promoter KST1 and examined those plants using growth room and greenhouse experiments. The expression of AtHXK1 in tobacco guard cells reduced stomatal conductance and transpiration by about 25% with no negative effects on photosynthesis or growth, leading to increased water-use efficiency. In addition, these plants exhibited tolerance to drought and salt stress due to their lower transpiration rate, indicating that improved stomatal function has the potential to improve plant performance under stress conditions

Sucrose Synthase and Fructokinase Are Required for Proper Meristematic and Vascular Development

Sucrose synthase (SuSy) and fructokinase (FRK) work together to control carbohydrate flux in sink tissues. SuSy cleaves sucrose into fructose and UDP-glucose; whereas FRK phosphorylates fructose. Previous results have shown that suppression of the SUS1,3&4 genes by SUS-RNAi alters auxin transport in the shoot apical meristems of tomato plants and affects cotyledons and leaf structure; whereas antisense suppression of FRK2 affects vascular development. To explore the joint developmental roles of SuSy and FRK, we crossed SUS-RNAi plants with FRK2-antisense plants to create double-mutant plants. The double-mutant plants exhibited novel phenotypes that were absent from the parent lines. About a third of the plants showed arrested shoot apical meristem around the transition to flowering and developed ectopic meristems. Use of the auxin reporter DR5::VENUS revealed a significantly reduced auxin response in the shoot apical meristems of the double-mutant, indicating that auxin levels were low. Altered inflorescence phyllotaxis and significant disorientation of vascular tissues were also observed. In addition, the fruits and the seeds of the double-mutant plants were very small and the seeds had very low germination rates. These results show that SUS1,3&4 and FRK2 enzymes are jointly essential for proper meristematic and vascular development, and for fruit and seed development

Sucrose-induced stomatal closure is conserved across evolution.

As plants evolved to function on land, they developed stomata for effective gas exchange, for photosynthesis and for controlling water loss. We have recently shown that sugars, as the end product of photosynthesis, close the stomata of various angiosperm species, to coordinate sugar production with water loss. In the current study, we examined the sugar responses of the stomata of phylogenetically different plant species and species that employ different photosynthetic mechanisms (i.e., C3, C4 and CAM). To examine the effect of sucrose on stomata, we treated leaves with sucrose and then measured their stomatal apertures. Sucrose reduced stomatal aperture, as compared to an osmotic control, suggesting that regulation of stomata by sugars is a trait that evolved early in evolutionary history and has been conserved across different groups of plants

Guard-cell-targeted overexpression of Arabidopsis Hexokinase 1 can improve water use efficiency in field-grown tobacco plants

Water deficit currently acts as one of the largest limiting factors for agricultural productivity worldwide. Additionally, limitation by water scarcity is projected to continue in the future with the further onset of effects of global climate change. As a result, it is critical to develop or breed for crops that have increased water use efficiency and that are more capable of coping with water scarce conditions. However, increased intrinsic water use efficiency (iWUE) typically brings a trade-off with CO2 assimilation as all gas exchange is mediated by stomata, through which CO2 enters the leaf while water vapor exits. Previously, promising results were shown using guard-cell-targeted overexpression of hexokinase to increase iWUE without incurring a penalty in photosynthetic rates or biomass production. Here, two homozygous transgenic tobacco (Nicotiana tabacum) lines expressing Arabidopsis Hexokinase 1 (AtHXK1) constitutively (35SHXK2 and 35SHXK5) and a line that had guard-cell-targeted overexpression of AtHXK1 (GCHXK2) were evaluated relative to wild type for traits related to photosynthesis and yield. In this study, iWUE was significantly higher in GCHXK2 compared with wild type without negatively impacting CO2 assimilation, although results were dependent upon leaf age and proximity of precipitation event to gas exchange measurement

Effect of <i>SlSUS</i> suppression on tomato fertility and seed viability.

<p><b>(A)</b><i>SlSUS-RNAi</i> and WT plants were grown in a greenhouse to maturity. Flowers from the first five inflorescences from the ground of each plant (<i>n</i> = 9) were counted. <b>(B)</b> Fruit set was calculated as the number of fruit divided by the number of flowers from the first five inflorescences of each plant (<i>n</i> = 9). <b>(C)</b> To calculate average seed weights, 50 seeds per fruit (<i>n</i> = 4) were counted and weighed, and that weight was divided by the number of seeds. Error bars represent the standard error. Asterisks indicate a statistically significant difference relative to the WT (* <i>P</i> < 0.05; ** <i>P</i> < 0.01).</p

Guard-cell-targeted overexpression of Arabidopsis Hexokinase 1 can improve water use efficiency in field-grown tobacco plants.

Water deficit currently acts as one of the largest limiting factors for agricultural productivity worldwide. Additionally, limitation by water scarcity is projected to continue in the future with the further onset of effects of global climate change. As a result, it is critical to develop or breed for crops that have increased water use efficiency and that are more capable of coping with water scarce conditions. However, increased intrinsic water use efficiency (iWUE) typically brings a trade-off with CO2 assimilation as all gas exchange is mediated by stomata, through which CO2 enters the leaf while water vapor exits. Previously, promising results were shown using guard-cell-targeted overexpression of hexokinase to increase iWUE without incurring a penalty in photosynthetic rates or biomass production. Here, two homozygous transgenic tobacco (Nicotiana tabacum) lines expressing Arabidopsis Hexokinase 1 (AtHXK1) constitutively (35SHXK2 and 35SHXK5) and a line that had guard-cell-targeted overexpression of AtHXK1 (GCHXK2) were evaluated relative to wild type for traits related to photosynthesis and yield. In this study, iWUE was significantly higher in GCHXK2 compared with wild type without negatively impacting CO2 assimilation, although results were dependent upon leaf age and proximity of precipitation event to gas exchange measurement.This work was supported by the project Realizing Increased Photosynthetic Efficiency (RIPE), that is funded by the Bill & Melinda Gates Foundation, Foundation for Food and Agriculture Research (FFAR), and the UK Foreign Commonwealth and Development Office under grant number OPP1172157

Suppression of sucrose synthase affects auxin signaling and leaf morphology in tomato

<div><p>Metabolic enzymes have been found to play roles in plant development. Sucrose synthase (SUS) is one of the two enzyme families involved in sucrose cleavage in plants. In tomato, six SUS genes have been found. We generated transgenic tomato plants with RNAi suppression of <i>SlSUS1</i>, <i>SlSUS3</i> and <i>SlSUS4</i> genes. Independent transgenic lines with RNAi suppression of more than one <i>SUS</i> gene exhibited morphological effects on their cotyledons and leaf structure, but there were no significant effects on their carbohydrate levels, demonstrating that SUS has a developmental function, in addition to its metabolic function. Shoot apices of the transgenic lines showed elevated expression of <i>JAGGED</i> (<i>JAG</i>) and the auxin transporter <i>PIN1</i>. In a PIN1-GFP fusion reporter/SUS-RNAi hybrid, PIN1-GFP patterns were altered in developing leaves (as compared to control plants), indicating that <i>SlSUS</i> suppression alters auxin signaling. These results suggest possible roles for SUS in the regulation of plant growth and leaf morphology, in association with the auxin-signaling pathway.</p></div

<i>SlSUS-RNAi</i> lines exhibit <i>SlSUS</i> co-suppression.

<p><b>(A-C)</b> Reduced expression of <i>SlSUS</i> genes. RNA was extracted from green fruits, shoot apices, and mature leaves of <i>SlSUS-RNAi</i> and WT lines. cDNA was generated and subjected to real-time PCR analysis, using primers specific for <i>SlSUS1</i>, <i>3</i> and <i>4</i>. Cyclophilin was used as a reference gene. Error bars indicate the standard error (<i>n</i> ≥ 3). Asterisks indicate a statistically significant difference from the WT (* <i>P</i> < 0.05; ** <i>P</i> < 0.01).</p